Detection: Cisco Isovalent - Non Allowlisted Image Use

Updated Date: 2026-01-05 ID: 9f2b7b1d-6c2f-4f2d-9a8b-8a1d7c5f2e11 Author: Bhavin Patel, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects use of container images that fall outside an approved allowlist, leveraging Cisco Isovalent/Tetragon runtime telemetry (image name and workload identity). Adversaries commonly introduce untrusted or newly published images to deploy tooling, establish persistence, or abuse supply‑chain trust. This behavior may indicate image pulls from unauthorized registries, execution of unvetted software, or a drift from established deployment baselines. Extra scrutiny is warranted for namespaces and workloads that normally source images from restricted registries, and for pods that suddenly begin running images outside expected prefixes. Maintain an environment‑specific allowlist via the macro cisco_isovalent_allowed_images (for example, allow trusted registries/prefixes such as ImageName="gcr.io/org/", "registry.local/", or "myco/*") and keep it updated as new baseline images are introduced. This analytic alerts on images NOT matching the allowlist.

Search

 1`cisco_isovalent_process_exec` pod_name!=""
 2
 3| search NOT `cisco_isovalent_allowed_images`
 4
 5| stats count 
 6        min(_time) as firstTime 
 7        max(_time) as lastTime 
 8    by pod_image_name pod_namespace pod_name process_name cluster_name
 9
10| `security_content_ctime(firstTime)`
11
12| `security_content_ctime(lastTime)`
13
14| `cisco_isovalent___non_allowlisted_image_use_filter`

Data Source

Name	Platform	Sourcetype	Source
Cisco Isovalent Process Exec	Other	`'cisco:isovalent:processExec'`	`'not_applicable'`

Macros Used

Name	Value
cisco_isovalent_allowed_images	`pod_image_name IN ("docker.io/library/ubuntu:22.04","docker.io/grafana/grafana:12.0.1", "quay.io/isovalent-dev/tetragon-ci","quay.io/isovalent/tetragon-ci","quay.io/isovalent/hubble-export-fluentd*")`
cisco_isovalent___non_allowlisted_image_use_filter	`search *`

cisco_isovalent___non_allowlisted_image_use_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1204.003	Malicious Image	Execution

Installation

DE.AE

CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

The detection is based on process execution data generated by Cisco Isovalent Runtime Security. Ensure that Isovalent Runtime Security is deployed and configured in your Kubernetes environment to emit process_exec events. Configure the Cisco Security Cloud TA to collect these logs via HTTP Event Collector (HEC) and normalize them into the Splunk Common Information Model. This integration ensures that all relevant pod, container, and process activity is captured for monitoring and detection of suspicious behavior. Create and maintain an environment‑specific macro namedcisco_isovalent_allowed_images that returns true for approved images, for example:(ImageName="gcr.io/org/app:" OR ImageName="registry.local/" OR ImageName="myco/*"). The search alerts on images NOT matching that allowlist. Tune by namespace or team as needed.

Known False Positives

New legitimate images during rollouts or blue/green deployments may appear until the allowlist is updated. Coordinate with platform/DevOps teams to synchronize allowlist changes.

Associated Analytic Story

Cisco Isovalent Suspicious Activity

Risk Based Analytics (RBA)

Risk Message:

Non Allowlisted image [$pod_image_name$] used by pod [$pod_name$] in the cluster [$cluster_name$]

Risk Object	Risk Object Type	Risk Score	Threat Objects
pod_name	system	45	process_name

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`not_applicable`	`cisco:isovalent:processExec`
Integration	✅ Passing	Dataset	`not_applicable`	`cisco:isovalent:processExec`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1